The following correction was printed in the Guardian's Corrections and clarifications column, Thursday April 12 2007

In the article below, Labour lost the February 2006 byelection in Dunfermline and West Fife to the Liberal Democrats and not to the SNP. Holyrood, not Hollyrood, is the site of the Scottish parliament (not assembly).

Sometimes history has a sense of humour. On May 1, we shall mark (celebrate or mourn, according to taste) the 300th anniversary of the union between England and Scotland. The following day we shall mark (ditto) the 10th anniversary of Tony Blair's prime ministership.

And the day after that, it seems certain that the largest number of seats in the Edinburgh assembly will be won by the Scottish National party on a platform of national independence, which was specifically what devolution was meant to avert. As if that weren't rich enough, only weeks later the member for Kirkcaldy and Cowdenbeath will probably become prime minister and inherit a mixture of political and constitutional crisis.

All this comes on top of more polls which show, to a degree that must surprise even Gordon Brown's enemies, how much he is distrusted by the electorate. Whatever his successes with the economy, his career has been one of personal political failure, from 1994 when he wasn't even supported by a majority of Scottish MPs, to February of last year, when he campaigned hard in the Dunfermline West byelection on his doorstep, and Labour lost the seat to the SNP. His problems now transcend the West Lothian question, though that will be brightly highlighted by the first occupant of No 10 since 1964 to represent a Scottish constituency. Brown will then be in the weird position of being not merely an MP, but a prime minister, able to vote on English legislation and not on laws affecting his own constituency.

After May 3 there are large developments impending, and drastic remedies will be sought. One comes to mind. The "Ausgleich" of 1867 was the "balance" between the two parts of what had been a unitary state but which, thanks to that compromise, became the dual monarchy of Austria-Hungary. Is it now time for a British Ausgleich?

Mutual resentment has grown in the past half-century. As recently as 1955, when the Tories not only won power at Westminster but won a majority of Scottish seats, there was no logical ground for Scottish disaffection. But it blossomed in the 60s and 70s, and during the Thatcher years, when the Scots were ruled by a government only a minority of them had voted for. Labour hoped that devolution would appease that sentiment, but it has conspicuously failed to do so: just as the nationalists hoped, many Scots have acquired a taste for greater autonomy.

In England, anger has also grown. Writing in the London Review of Books, Neal Ascherson is dismayed to find in London "a bout of Scotophobia without parallel since the violently anti-Scottish mood of the English mob in Lord Bute's day". But is this really so surprising? Disquiet is, after all, found even among politicians who once supported devolution. On these very pages Roy Hattersley, a former deputy Labour leader and not a rabid Scotophobe, has written that it is a "constitutional absurdity" for a Scottish MP to be home secretary. So it is, but John Reid's position is absurd because of devolution. Without going back as far as Peel (who was home secretary before the reform bill while sitting for an Irish pocket borough), there was no objection to Asquith as home secretary in 1892-95 when he sat for Fife, or Churchill in 1910-11 when he was member for Dundee, any more than there was, in principle, to a premier sitting for a Scottish or Welsh seat.

Everything has changed since the Hollyrood assembly, which has made the character of the present London government beyond absurdity. Writing on the Guardian website, the Scottish political journalist Iain MacWhirter is also taken aback by English ire. "The idea of a Scottish raj running England," he thinks, is surely "so extraordinary" as to defy comment.

But is it? There are 23 members of the present cabinet. If you take away the prime minister (born and educated in Scotland) and the two peers (one of them another Scot, Lord Falconer, the lord chancellor of England), that leaves 20 - of whom five are MPs for Scottish seats. Given that the Scots are no more than one-twelfth of the UK's population, to have a quarter-Scottish cabinet would be hard to defend even before devolution; it is now plainly ludicrous. Is it any wonder that an ICM poll last November found 59% of people in England would prefer Scotland to be independent?

But other things have changed. Alex Salmond, the SNP leader, now says that he wants England to remain "Scotland's best friend", and that he doesn't expect absolute separation, which would anyway be less than total thanks to common membership of the EU. He is happy to keep sterling as the Scottish currency, he says, and for that matter to keep the monarchy. This would take us back to the 17th century: between the accession of James I and VI in 1603 and the union 104 years later, there was a "union of crowns", but the two countries were distinct in their internal government. Or back to what was once envisaged as a settlement of the Irish question. Under the first home rule bill of 1886, Ireland was to have its own parliament in Dublin - and there was to be no further Irish representation at Westminster. Although I have not seen this spelled out by any historian, that arrangement must surely have been influenced by the Ausgleich only nine years earlier.

To many people in both countries, "England-Scotland", with two separate parliaments, must seem increasingly attractive. It would remove the huge grievance of Scottish MPs at Westminster who have no purpose but to force through unpopular English legislation and collect their expenses. Whether the Black Watch would be serving in Basra after such a settlement is another question, although when Salmond calls Iraq Blair's greatest crime he is speaking for most people south as well as north of the Tweed.

You can judge Brown's panic at the coming constitutional crisis by the hysterical manner in which he has been campaigning in Scotland, warning that if the SNP win they will claim not only a share of oil revenues but their own Olympic team. Why, next thing Salmond will be the Caledonian Ahmadinejad, demanding his own nuclear weapons.

As Severin Carrell wrote in yesterday's Guardian, reporting on the Scottish election, Brown is facing the toughest years of his political career - and a predicament of Labour's own making. He may not be quite the last prime minister of the UK, but it would be a nice irony if he were.